1. What is conductivity and how is it measured?

Conductivity simply is a material's ability to allow something to flow through it. There are two main types:

Electrical conductivity: This refers to how easily electricity can pass through a material. Metals, with freely moving electrons, are good conductors, while insulators like rubber have very low electrical conductivity. The electrical conductivity is measured using a conductivity meter. It applies a voltage to the material and measures the resulting current. The higher the current, the higher the conductivity.

Thermal conductivity: This describes how well a material conducts heat. Metals are again good conductors, efficiently transferring heat, whereas materials like wood are poor conductors, making them good insulators. Measuring thermal conductivity requires a heat flow meter to measure the amount of heat flowing through a material under a specific temperature difference.

2. What are the units of conductivity measurement?

The units of conductivity measurement are siemens per meter (S/m) or millisiemens per centimeter (mS/cm).

3. How do temperature changes affect conductivity readings?

Conductivity is directly proportional to temperature. As temperature increases, the movement of ions also increases, which leads to a higher conductivity reading. Therefore, it is important to calibrate the conductivity meter at the same temperature as the sample.

Temperature can significantly impact conductivity readings, especially in solutions, readings are often reported at a standard temperature (usually 25° C). This allows for accurate comparisons of conductivity between different samples or measurements taken at different times.

Some conductivity meters have built-in temperature compensation features that automatically adjust the reading based on the measured temperature.

4. How often do I calibrate a conductivity measuring setup?

The ideal calibration frequency for a conductivity measuring set up depends on several factors:

Manufacturer recommendations: Your conductivity system manufacturer will likely have specific recommendations for calibration frequency. Consult your user manual or contact the manufacturer for their advice.

Frequency of use: Frequently used systems (every day or several times a week) may need calibration more often than those used once a month or less.

Environmental factors: Set up used in harsh environments (extreme temperatures, corrosive chemicals) might require more frequent calibration to ensure accuracy.

Sample type: High-purity or low-conductivity samples may require less frequent calibration compared to those with high concentrations of ions or impurities. Mettler Toledo provides specialty sensors for ultra-pure water and low conductivity samples. These sensors have certified cell constant and do not need to be calibrated by the users.

Desired accuracy: If very high accuracy is critical for your application, you might choose to calibrate more frequently for peace of mind.

As a general guideline:

Minimum: Most manufacturers recommend calibration at least once a year.

Typical: For frequent use in standard conditions, calibration every three to six months is a good practice.

More frequent: If any of the factors above apply (harsh environment, high-precision needs), consider calibrating every one to three months.

Additional signs your meter might need calibration:

  • Unexpected changes like verification results are out of range in conductivity readings of your samples.
  • Inconsistent or unreliable readings.
  • Long time since the last calibration (even if use has been minimal).
  • Suspected damage to the meter.

By following these guidelines and being attentive to a meter's performance, you can ensure it delivers accurate and reliable conductivity measurements.

5. What is the importance of maintaining proper electrode care and maintenance for conductivity measurements?

Proper electrode care and maintenance are essential to obtain accurate conductivity measurements. The electrodes should be kept clean and free from contamination. They should be stored in dry when not in use. Regular calibration and verification of the electrodes should also be performed.

6. What is the relationship between conductivity and the concentration of ions in a solution?

The conductivity of a solution is directly proportional to the concentration of ions in the solution. A higher concentration of ions in a solution leads to a higher conductivity value.

Download our free conductivity guide for a quick and easy guide on how to perform pH calibration. Also, click here to learn more about conductivity measurement setup to perfectly match your specific application.

To contact the author of this article, email pHmatters@mt.com